Agriculture, Slavery

If we look at a slave as a economic unit, you have to get more out of him economically then you put in. Only in an agrarian setting is this possible. Rome, Ottomans all had slaves. In the US South slaves were used to pick cotton. Slavery really did not have anything to do with skin color - my guess is in US it was preferred, because Africa was on one of the trade routes, plus, in a white society it was easier to identify slaves if they were in different color, that could have been another reason for black slavery in America. But otherwise there was slavery of all kinds around the Mediterranean - white or black.

Link

[During the years of the Roman Empire a] fairly large percentage of the people living in Rome and Italy were slaves. Historians aren't sure of an exact percentage but somewhere between 20% and 30% of the people were slaves. During the early parts of the Roman Empire, as many as one third of the people in Rome were slaves.

Rifkin

Slave labor built the great pyramids of Egypt, the Great Wall of China, and the ceremonial shrines of the Mayan and Teotihuacan civilizations in the Americas. The Great Wall in China required the labor of more than a million slaves, half of whom perished in the effort. Nearly 20 percent of the population of Rome in the first few centuries A.D. were slaves.

Whereever there is agriculture, there is slavery.

Think about it; could there be slavery pre-agro? Let's say you wanted to make a fellow forager a slave.. u pick a little guy, your mini-me, u smack'em around, he makes you laugh... But now you have to take care of this other person, need to hunt twice as much to obtain food. If he hunted, foraged by himself, he can't be slaved. So economically, slavery before farming makes no sense. Only through landowning, farming you can create a surplus some of which you can use to hire guards, overseers, managing labor which then creates even more surplus.